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METHODS OF STUDYING THE CONCENTRATION AND 
COMPOSITION OF THE SOIL SOLUTION 



F. W. PARKER 

M 

UNIVERSITY C0NS1N 
PH.D. THESIS iqM 



Agricultural Experiment Station, University of Wisconsin 



Reprinted from 

Soil Science, Vol. XII, No. 3, September. 1921 



LIBRARY OF CONGRESS 
•CEIVED 

APR 6 1922 

DOCUMENTS DtVidlOfc 



d 



f 



a5 



Reprinted from Sou. Scibncb 
Vol. XII, No. 3, September, 1921 



6^ 



METHODS OF STUDYING THE CONCENTRATION AND 
COMPOSITION OF THE SOIL SOLUTION 1 

F. W. PARKER 

Agricultural Experiment Station, University of Wisconsin 
Received for publication March 7, 1921 

A more exact knowledge of the soil solution is desirable for the study of 
many of the problems of soil fertility and related subjects. The purpose of 
the present investigation was to study some of the methods which have been 
used in determining the concentration and composition of the soil solution 
and to compare the results obtained by the different methods. 

The methods which have been used may be classified into groups as follows: 

(a) Methods involving extraction with comparatively large amounts of 
water. 

(b) Methods which aim to obtain the true soil solution. 

(c) Methods which aim to measure the concentration of the soil solution 
directly in the soil. 

The water-extraction method has been widely used and possesses many 
advantages. The greatest criticism of the method is that the addition of a 
large quantity of water alters the equilibrium in the soil. It undoubtedly has 
a solvent effect and may also cause a precipitation of some of the material in 
solution due to an alteration in the nature of the solvent. The quantity of 
salts obtained depends upon a number of factors. Mitscherlich (17) has shown 
the effect of the C0 2 content of the water, the time of extraction, and the 
ratio of soil to water on the quantity of material extracted. The procedure is 
arbitrary, but results obtained by several investigators indicate that the usual 
1 :5 extraction gives an approximate measure of the salt content of the soil 
solution. 

Because of the lack of knowledge as to whether or not the water extraction 
gives a good quantitative measurement of the salts in the soil, there have 
been several methods proposed for obtaining the true soil solution. 

Ramann, Marz and Bauer (21) have obtained the soil solution by the use 
of a hydraulic press. They applied a pressure of about 4,000 pounds to the 
square inch. Lipman (16) also used the pressure method, applying a maxi- 

1 Part 1 of a thesis submitted at the University of Wisconsin in partial fulfillment of the 
requirements for the degree of Doctor of Philosophy. Published with the permission of the 
Director of the Wisconsin Agricultural Experiment Station. 

The writer wishes to express his appreciation for the helpful suggestions and criticisms 
tendered by Prof. E. Truog. 

209 



210 F. W. PARKER 

mum pressure of 53,000 pounds to the square inch. The method is of limited 
value for it is only applicable to finer-textured soils at a rather high moisture 
content and requires a complicated apparatus. The criticism has been made 
by Northrup (19) that the application of high pressures such as were used by 
Lipman would alter the physico-chemical equilibrium in the soil and as a 
result the true soil solution would not be secured. 

The centrifuge method of Briggs and McLane (23) and the artificial root 
method of Briggs and McCall (8), in which suction is used, may give the true 
soil solution. However, these methods are only applicable to soils at high 
moisture contents and only small amounts of the solution are obtained. 

The displacement method was first used by Schloesing (22). He used water 
colored with carmine to displace the soil solution and obtained considerable 
amounts which were used for analytical purposes. Gola (9) used water as 
the displacing liquid in his studies on the concentration of the soil solution. 
Ischerekov (15) used ethyl alcohol as the displacing liquid and obtained 
results which indicate that the displaced solution is the true soil solution in an 
unaltered condition. Moist soil was packed in a glass tube which had a piece 
of linen tied over the bottom. After placing alcohol on top of the soil column 
the soil solution soon began to drop from the bottom of the tube. He reports 
results which indicate that the successive portions of the displaced solution 
are of the same composition, and that the concentration of the soil solution 
is inversely proportional to the moisture content of the soil. 

Van Suchtelen (25) modified Ischerekov's method by using paraffin oil as 
the displacing liquid and applying suction to hasten displacement. Morgan 
(18) used a combination of the pressure and displacement methods in which 
a heavy oil was used as the displacing liquid and applied pressures of about 
500 pounds to the square inch to force the oil into the packed soil. Large 
quantities of the soil solution were thus obtained. The method is open to the 
objection that it requires a complicated apparatus and the use of a heavy 
oil makes it uncleanly. 

The writer has been unable to find any reference in the literature in which 
a comparison was made of the results obtained by the displacement and 
water-extraction methods. 

Several methods have been suggested for determining the concentration of 
the soil solution directly in the soil. Among the first of these was the meas- 
urement of the salt content by electrical conductance (10). The method is 
of some use in determinations of alkali in soils but the results are affected by 
the texture, organic matter, carbonates, and the moisture content of the soil. 
It has not proved of any great value in investigational work. 

Bouyoucos and MciCool (5, 6) have advanced the freezing-point method as 
a means of determining the concentration of the soil solution directly in the 
soil, and as a means of measuring the absolute salt content of the soil (7). 
The results obtained by this method will be discussed in the latter portion of 
this paper. 



CONCENTRATION AND COMPOSITION OF SOIL SOLUTION 211 

In the present investigation a study was made of the displacement and 
freezing-point methods. The results obtained by displacement are compared 
with those obtained by the freezing-point and water-extraction methods. 

THE DISPLACEMENT METHOD 

Description of the 'method and procedure 

The method consists of packing the moist soil in a cylinder provided with 
an outlet at the bottom. The displacing liquid is then poured on top of the 
soil column and as it penetrates the soil it displaces some of the soil solution 
which forms a zone of saturation below the displacing liquid. This zone 
increases in depth as it is continually forced downward by the pressure of the 
liquid above. When the saturated zone reaches the bottom of the soil column 
the clear soil solution, free of alcohol, drops from the soil as gravitational 

water. 

The only apparatus required is a cylinder in which to pack the soil. The 
diameter of the soil column very largely determines the rate at which the 
soil solution will be obtained. The height of the soil column likewise deter- 
mines the time required for displacement. These two factors must be con- 
sidered in the selection of the cylinder to be used. 

Three different-sized cylinders were used in the present investigation. 
Brass soil tubes 2 inches in diameter and 9 or 12 inches in depth were used in 
the preliminary work and when only small amounts of the soil solution were 
desired. Large brass soil tubes 3 inches in diameter were used for securing 
larger quantities of the solution and in studying the composition of successive 
portions of the displaced solution. These tubes were made in 6-inch sections 
and three or four sections were generally used. The bottom section was 
provided with a false screen bottom and a small outlet. Glass percolators, 
2| inches in diameter at the top and 15 inches deep, were used in most of the 
work. The bottom of the percolator was fitted with a small one-hole stopper. 
A small quantity of coarse quartz sand was placed in the percolator before 
adding the soil. 

The soil was packed in the tubes by means of a short wooden rod. No 
difficulty was experienced in obtaining uniform packing. The degree of pack- 
ing is determined by the kind of soil and its moisture content. Sandy soils 
were packed as firmly as possible at all moisture contents. Peats also may be 
packed firmly, for there is no danger of puddling the soil and rendering it 
impervious to the displacing liquid. With the heavier classes of soil care 
must be taken to prevent puddling during the packing, in which case the rate 
of displacement is exceedingly slow or entirely prevented. For this reason 
it is best to use the heavier soils at a moisture content somewhat below the 
optimum for plant growth. Under proper moisture conditions the soil should 
not stick together too readily when squeezed in the hand but should be rather 
granular and easily worked. Miami silt loam was best used at a moisture 



212 F. W. PARKER 

content of about 20 per cent and when properly packed had an apparent 
specific gravity of 1.50 to 1.60. After a little experience one can readily 
determine the proper degree of packing for any soil at a given moisture content. 

After packing, the cylinders were placed in ring stands and the displacing 
liquid added and maintained at a depth of 2 to 3 inches. 

The time required for displacement varied widely, depending on the mois- 
ture content of the soil, the degree of packing, the soil type and the height of 
the soil column. In most cases it is possible to complete the displacement in 
12 hours if the height of the soil column is not over 12 or 14 inches. The 
displacement may be stopped at any time by removing the layer of the dis- 
placing liquid on top of the soil column. In some cases the displacement 
was started in the evening and completed the next day. When silt loam soils 
were very firmly packed it sometimes required several days to complete the 
displacement. 

In the water-extraction method the extracts were made by adding the 
desired amount of distilled water to the soil in a large mortar and stirring for 
3 minutes. After settling 12 minutes the suspension was filtered through 
Pasteur-Chamberland filters. 

In the displacement method nitration is unnecessary and total salts were 
determined by evaporating 25 cc. of the soil solution in a platinum crucible. 
In the water-extraction method larger quantities were evaporated in plat- 
inum dishes. After evaporation the crucibles and dishes were placed in an 
electric oven at 105°C. for 12 hours. The weight of the residue represented 
total salts before ignition. The crucible and contents were then ignited to 
constant weight to determine the total salts after ignition. 

Nitrates were determined colorimetrically by the phenoldisulfonic acid 
method. 

Calcium was determined volumetrically by titration of the oxalate with 
potassium permanganate. 

Freezing-point determinations were made in the usual manner with a 
Beckman thermometer. 

The effect of different displacing liquids on the time and percentage displacement 

Water, ethyl alcohol, and paraffin oil were the liquids employed by previous 
investigators who used the displacement method. It seemed desirable to 
try other liquids to determine which would give the most complete and rapid 
displacement. In the preliminary work it was found that liquids which were 
non-miscible with water such as benzene, kerosene, ligroin, and ethyl acetate 
would not satisfactorily displace the soil solution. These liquids passed 
through the soil in practically an unaltered condition and displaced practically 
none of the soil solution. To use these liquids it would be necessary to pack 
the soil more and use pressure, as was done by Morgan (18). 

The four liquids studied were ethyl alcohol, methyl alcohol, acetone a'nd 
water. Miami silt loam at a moisture content of 21 per cent was packed in 



CONCENTRATION AND COMPOSITION OF SOIL SOLUTION 



213 



four 3-inch brass cylinders, care being taken to obtain uniform packing. The 
degree of packing in these cylinders was not great enough to obtain the most 
complete displacement. The time which elapsed between the addition of the 
displacing liquid and the appearance of the first drop of the soil solution was 
recorded. The volume of the water in the soil being known, the percentage 
displaced was readily calculated from the volume of the solution obtained. 
In order to detect the first appearance of the displacing liquid in the soil 
solution a freezing-point determination was used. The freezing point of 
successive portions of the solution was determined. As soon as the displacing 
liquid appeared in the solution the freezing point was appreciably changed. 
The appearance of ethyl alcohol and acetone was further confirmed by quali- 
tative tests. 

Table 1 shows the effect of different liquids on the time and percentage dis- 
placement. The viscosity of the liquids also is given in the table, since vis- 
cosity is one of the main factors influencing the time and percentage displace- 
ment. The less viscous displacing liquids pass through the pore spaces of 

TABLE 1 

The time and percentage displacement of the soil solution from Miami silt loam by different 

liquids 



DISPLACING LIQUID 


VISCOSITY IN C. C. S. 
UNITS AT 20°C. 


TIME TO THE FIRST 
DROP 


DISPLACEMENT 




0.00334 
0.00591 
0.01006 
0.01190 


hrs. 
2 

4 
4* 


per cent 

12.0 




24.0 




20.0 




36.0 




- 



This causes them to 



the soil more readily than do the more viscous liquids, 
mix with a greater portion of the soil solution. 

These and similar results obtained with other soils indicate that ethyl alco- 
hol is the most satisfactory displacing liquid. It gives a more complete 
displacement than the other liquids used and it is very easy to test for its 
appearance in the displaced solution by means of the iodoform reaction. 

Water is a fairly satisfactory displacing liquid but it mixes more with the 
soil solution and does not give as complete a displacement as does ethyl alco- 
hol. If water is used some NaCl should be added making it possible to 
determine when the displacing solution appears by testing with silver nitrate. 

Acetone is not at all satisfactory for it has too low a viscosity and therefore 
passes through the soil too readily, giving a very low percentage displacement. 
Methyl alcohol possesses no marked advantage over water and is not as good 
as ethyl alcohol. 

Before ethyl alcohol was selected for subsequent work, additional experi- 
ments were made to determine the percentage displacement that would ordi- 
narily be obtained by its use. The percentage displacement depends upon 



214 



F. W. PARKER 



several factors. The higher the soil column and the more compact the soil, 
the greater will be the percentage of the soil solution displaced. A high mois- 
ture content also tends to produce a high percentage displacement. How- 
ever, these same factors determine very largely the time required for dis- 
placement, and the time element should not be made too great. 

The experiments indicated that it was practicable with most soils to obtain 
from 35 to 45 per cent of the soil solution by displacement with ethyl alcohol. 
This amount may be secured without the time element becoming very objec- 
tionable. It is possible to displace a much greater percentage than this. 
Using a silt loam soil at a moisture content of 23.3 per cent, a 75.6 per cent 
displacement was secured. Ischerekov (15) reports that with a soil at satura- 
tion it is possible to displace 95 per cent of the soil solution. 



The concentration of the soil solution obtained by the use of different displacing 

liquids 

A consideration of the mechanics of displacement leads to the conclusion 
that the soil solution obtained is in all cases really displaced by the soil solu- 

TABLE 2 

The concentration of the soil solution obtained with different displacing liquids 



DISPLACING LIQUID 



Acetone 

Methyl alcohol 

Water 

Ethyl alcohol. . 



TOTAL SALTS IN SOLUTION 


FREEZING-POINT 






DEPRESSION 


Before ignition 


After ignition 


OP SOLUTION 


p. p. m. 


p. p. m. 


"C. 


655 


248 


0.020 


649 


246 


0.019 


670 


232 


0.020 


660 


248 


0.019 



tion itself. A zone, in which the soil is saturated with the soil solution, soon 
forms immediately below the displacing liquid after it is added. After the 
formation of this zone the only function of the displacing liquid is to give 
pressure and cause a downward movement of the saturated zone. Therefore, 
the displacing liquid should not affect the concentration of the solution 
obtained. The question of the influence of the displacing liquid on the con- 
centration of the solution was studied experimentally, using the solutions 
secured from Miami silt loam by the different liquids shown in table 1. The 
results are recorded in table 2 and confirm the conclusions reached by a theo- 
retical consideration of the question. 



Composition of successive portions of the displaced solution 

In displacement the soil solution moves through the soil. The first por- 
tions move only a short distance before they drop from the soil, while the last 
portion may pass through a soil column of considerable height. The question 



CONCENTRATION AND COMPOSITION OF SOIL SOLUTION 



215 



at once arises as to whether or not the movement of the soil solution through 
the soil alters its composition. If it does, successive portions of the dis- 
placed solution would not be of the same composition. If they are not of the 
same composition the method probably would be of little value. 

In a well mixed soil the solution in all portions is probably of the same 
composition. The readily soluble salts are in solution and this solution is in 
equilibrium with the surrounding solid material. As the solution is displaced 
and passes downward it comes in contact with more solution of the same com- 
position and concentration and with solid material of the same nature as that 
from which it was displaced. Therefore, the point of equilibrium should not 
change and the composition of the solution should not be altered by its pas- 

TABLE 3 

The freezing-point depression and total salts in successive portions of the soil solution from 

Miami silt loam 



PORTION 


FREEZING-POINT 
DEPRESSION 


TOTAL SALTS IN SOLUTION 




Before ignition 


After ignition 


1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 


0.024 

0.023 

0.024 

0.025 

0.024 

0.022 

0.022 

0.025 

0.076f 

0.098f 

0.163f 

0.309f 

0.444f 

0.689f 


p. p. m. 

480* 

352 

360 

324 

344 

344 

496* 


p. p. m. 
200* 

168 

176 

172 

180 

176 

256* 



* High results due to colloidal material. 

t High results due to alcohol in the solution. 

sage through a column of soil which has been well mixed before it is packed 
in the cylinder. Hoagland, Martin and Stewart (14) have shown that a water 
extract of a soil when concentrated and allowed to percolate through another 
portion of the same soil does not alter much in its composition. It is therefore 
probable that the composition of the true soil solution would not be changed 
in passing through a soil column. 

If the soil solution has a solvent effect on the soil particles during its passage 
through the soil, the last portions would be more concentrated than the first. 
To determine whether or not successive portions are of the same composition, 
as indicated by a determination of the freezing point and total salts, a 3-inch 
brass cylinder was filled with Miami silt loam containing 22 per cent moisture. 



216 F. W. PARKER 

The height of the soil column was 22 inches and 35.3 per cent of the soil solu- 
tion was obtained. During displacement, successive portions were secured 
and the freezing point determined. Then portions 1 and 2, 3 and 4, 5 and 6, 
etc., were combined and the total salts determined in these larger portions. 
Table 3 presents the results. 

The first portion contained a small amount of colloidal material which 
caused a high result for total salts in that portion. Small amounts of alcohol 
began to come through in the ninth portion, as is indicated by the freezing- 
point depression. However, the amount was so small that the total salts 
were not affected until the thirteenth portion. Then the solution became tur- 
bid due to colloidal material. 

The results show that successive portions are of the same composition. 
Results have also been obtained showing that successive portions contain the 
same amount of nitrate nitrogen. It is probable that a complete analysis of 
the successive portions would prove that they were of the same composition 
in all respects. These results agree with those obtained by Ischerekov (15) 
and Schloesing (22). Ischerekov determined total salts and Schloesing deter- 
mined nitrates. 

The concentration of the soil solution at different moisture contents 

In most soils the soil solution is very dilute. All readily soluble material 
is in solution even at low moisture contents. The solution is only saturated 
in respect to those minerals which are comparatively insoluble and have a 
low rate of solubility. Therefore, the addition of a small amount of water 
should not bring a very appreciable amount of material in solution. That 
soils are very insoluble and have a low rate of solubility has been shown by 
the work of Bouyoucos (2), in using the freezing-point method. That being 
the case, the concentration of the soil solution should be approximately 
inversely proportional to the moisture content of the soil. The displacement 
method is well adapted to such a study, for it can be used at a wide range of 
moisture contents. If the concentration of the soil solution obtained from a 
soil at different moisture contents is inversely proportional to the moisture 
content, it affords further proof that the method gives the true soil solution. 

The relation of the moisture content and the concentration of the soil solu- 
tion was studied in three soils. The soils had been in the greenhouse in a 
moist condition several weeks. Portions of the moist soil were weighed out; 
to some portions water was added to give the desired moisture content while 
others were allowed to dry to lower the moisture contents. Before packing 
in the percolators all portions except those at the higher moisture contents 
were passed through a coarse screen to insure thorough mixing. Displace- 
ment was started as soon after the addition of water as possible, usually within 
4 to 6 hours. 

Tables 4, 5 and 6 give the results obtained with Plainfield sand, Miami 
silt loam and Carrington silt loam. If the concentration is inversely propor- 



CONCENTRATION AND COMPOSITION OF SOIL SOLUTION 



217 



tional to the moisture content, the freezing-point depression of the solution 
multiplied by the moisture content of the soil will give a constant (D:M = 
K). Also the parts per million of total salts in the dry soil will be a constant. 

TABLE 4 

The freezing-point depression of the soil solution and the total salts in Plainfield sand at varying 

moisture contents 





FREEZING-POINT 




TOTAL SALTS IN SOIL 


MOISTURE CONTENT 


DEPRESSION 
OF SOLUTION 


K (D.M=K) 






Before ignition 


After ignition 


per cent 


"C. 




p. p. m. 


p. p. m. 


4.25 


0.045 


0.191 


62 


13.1 


6.31 


0.030 


0.189 


45 


13.7 


8.30 


0.022 


0.182 


57 


12.9 


10.70 


0.018 


0.192 


50 


14.7 


12.40 


0.014 


0.173 


49 


14.1 


15.00 


0.013 


0.195 


54 


15.1 



TABLE 5 

The freezing-point depression of the soil solution and the total salts in Miami silt loam at varying 

moisture contents 





FREEZING-POINT 




TOTAL SALTS IN SOIL 


MOISTURE CONTENT 


DEPRESSION 
OF SOLUTION 


K {D.M=K) 






Before ignition 


After ignition 


per cent 


"C. 




p. p. m. 


p. p. m. 


10.30 


0.039 


0.401 


116.8 


44.4 


13.55 


0.030 


0.406 


116.1 


47.1 


17.25 


0.022 


0.379- 


104.3 


43.4 


20.62 


0.018 


0.371 


108.9 


44.8 


29.41 


0.013 


0.382 






34.05 


0.012 


0.408 







TABLE 6 

The freezing-point depression of the soil solution and the total salts in Carrington silt loam a 1 

varying moisture contents 





FREEZING-POINT 




TOTAL SALTS IN SOIL 




DEPRESSION 
OF SOLUTION 


K (M-D=K) 






Before ignition 


After ignition 


per cent 


"C. 




p. p. m. 


p. p. m. 


8.77 


0.100 


0.877 


275 


94.0 


11.80 


0.071 


0.837 


253 


92.3 


13.95 


0.067 


0.934 


253 


94.2 


16.00 


0.045 


0.720 


252 


95.3 


18.55 


0.043 


0.797 


253 


96.0 



The results show that within experimental error K and the parts per mil- 
lion of total salts are constants. Assuming that the concentration of the 
soil solution is inversely proportional to the moisture content, as is undoubt- 



218 



F. W. PARKER 



edly very nearly the case, these results indicate that the true soil solution is 
obtained. Ischerekov (15) preformed a similar experiment and obtained 
results of the same order. 



A comparision of results obtained by displacement and water extraction 

In a study of any method it is desirable to compare results obtained by its 
use with those obtained by other methods. The water extraction method is 
the one most generally used in studying the soluble salt content of soils. It 
was therefore used as a means of further studying the results obtained by the 
displacement method. The two methods can not be expected to give the 
same results in all cases but the result should be of the same general order. 

All nitrates are readily soluble and undoubtedly a very nearly correct 
quantitative determination of the nitrate nitrogen in the soil solution is 

TABLE 7 
Nitrate nitrogen in the dry soil as determined by the water-extraction and displacement methods 





NITRATE NITROGEN IN THE DRY SOIL 


SOIL NUMBER 






Displacement method 


Water extraction 




p. p. m. 


p. p. m. 


1 


4.5 


4.0 


2 


54.6 


52.0 


3 


31.0 


34.0 


4 


103.3 


100.0 


5 


53.2 


50.0 


6 


63.3 


60.0 


7 


17.3 


20.0 


8 


38.0 


36.0 


9 


2.4 


2.8 


10 


6.9 


6.4 



secured by the usual 1.5 water extraction. Since all of the nitrates are prob- 
ably in the soil solution before the addition of water, it should be possible to 
obtain the same results for nitrates in the soil by using the two methods. 
The results obtained with the two methods on a number of soils from differ- 
ent field plots and the greenhouse are given in table 7. 

The two methods, within experimental error, give the same result for 
nitrate nitrogen in the soils. We may therefore conclude that the displaced 
solution is of the same nitrate concentration as the solution in the soil. It is 
also evident that the solution is of the same concentration as the soil solution 
remaining in the soil. If this were not the case the results for nitrates would 
not agree. Probably the only difference between the displaced solution and 
the same solution as it existed in the soil, is that when in the soil it was under 
the influence of a physical force, adhesion, which held it to the soil particles. 

A further comparison of the two methods was made by using Miami and 
Carrington silt loam and determining the total salts and calcium. The water- 



CONCENTRATION AND COMPOSITION OF SOIL SOLUTION 



219 



extraction method cannot be expected to give exactly the same results for 
total salts and calcium as the displacement method, since the addition of 
a very large amount of water undoubtedly affects to some extent the amount 
of material in solution. As several investigators (17, 24) have shown, the 
results obtained by water extraction depend largely upon the ratio of soil to 
water. Therefore, it seemed desirable to use varying ratios of soil to water 
in the present case. The results are given in tables 8 and 9. 

In both soils the displacement method gave higher results for total salts 
than either the 1:1 or 1:2 water extraction. Evidently the addition of these 

TABLE 8 
Total salts and calcium in Miami silt loam obtained by water extraction and displacement 



METHOD USED 



Displacement. . 
1:1 extraction. 
1:2 extraction. 
1 : 5 extraction . 
1 : 10 extraction 



AMOUNT IN THE DRY SOIL 



Total salts 
before ignition 


Total salts 
after ignition 


Calcium 


p. p. m. 


p. p. m. 


p. p. m. 


261 


100 


35.6 


211 


83 


27.1 


234 


94 


30.4 


311 


109 


38.6 


377 


145 


60.8 



TABLE 9 

Total salts and calcium in Carrington silt loam as determined by water extraction and 

displacement 





AMOUNT IN THE DRY SOU. 




Total salts 
before ignition 


Total salts 
after ignition 


Calcium 


Displacement 


p. p. m. 

551 
450 
470 
582 
646 


p. p. m. 
209 
173 
199 
238 
277 


p. p. m. 
53.9 


1 : 1 extraction 


63.4 


1 : 2 extraction 


64.2 


1 : 5 extraction 


73.1 


1 : 10 extraction 


78.5 







amounts of water to the soils caused a greater removal of soluble material 
from solution than was brought into solution by the solvent action of the 
water. This removal of material from solution is probably caused largely 
by precipitation due to the change in the nature of the solvent. When larger 
quantities of water were used the solvent action was greater than the precipi- 
tating effect. The point of balance of these factors will probably vary in 
different soils. It is probable that on some soils a 1 : 1 water extraction would 
give higher results than the displacement method. In the two soils studied 
the 1 : 5 water extraction gave approximately the same result for total salts 
as the. displacement method. 



220 



F. W. PACKER 



More calcium was obtained from Miami silt loam by displacement than by 
a 1:1 or 1:2 water extraction, but this relation does not hold in the case of 
the Carrington silt loam. This difference is probably due to the calcium 
being present in different forms in the two soils. The Miami silt loam used 
was only very slightly acid, while the Carrington silt loam was strongly acid. 
Some results obtained with phosphorus on these two soils indicate that the 
phosphorus content of the soil solution is much lower than would be indi- 
cated by the usual water extraction. 

The results indicate that the displacement method gives the true soil solu- 
tion. Further studies of this character should give considerable information 
regarding the value of the water-extraction method for determining the 



TABLE 10 



Total sails and nitrate nitrogen in different soils obtained by the water-extraction and displacement 

methods 



KIND OF SOIL 



Acid peat 

Neutral peat 

Clay loam 

Superior clay 

Plainfield sand 

Hancock sand 

Gray silt loam 

Miami silt loam. . . . 
Carrington silt loam 
Waukesha silt loam. 



NO3 NITROGEN 



Displace- 
ment 



p. p. m. 

791.0 
745.0 

75.2 
24.7 
22.4 
61.2 
9.7 
71.0 
54.5 
30.4 



Extraction 



p. p. m. 

840.0 
690.0 
71.5 
29.4 
18.7 
57.0 
10.8 
79.8 
48.3 
30.4 



TOTAL SALTS IN THE DRY SOIL 



Before ignition 



^enT- ^traction 



p. p. m. 

7,484 
8,940 
747 
301 
275 
1,512 
161 
648 
512 
340 



p. p. in. 

11,374 

7,497 

796 

370 

205 

1,400 

223 

732 

. 506 

462 



After ignition 



^enf- fraction 



p. p. til. 

2,530 

3,233 

252 

87 

75 

348 

57 

222 

173 

119 



p. p. m. 

3,965 

2,618 

281 

121 

60 

325 

124 

256 

168 

186 



soluble material in a soil. Before final conclusions can be made regarding 
the value of the water-extraction method as compared with displacement 
further investigations will be necessary. These should include determina- 
tions of the phosphorus, potassium, calcium and magnesium in a large number 
of soils by the two methods. 

A further comparison of the two methods was made on ten soils by using 
the 1:5 water extraction on all except the peats. A 1: 10 extract was made 
with the acid peat and a 1 : 7.5 extract with the neutral peat. The results are 
shown in table 10 and confirm the conclusions drawn from the preceding data. 
With some soils the displacement method gave higher results for total salts, 
while with other soils the water extraction gave the higher results. The 
results for nitrate nitrogen are the same, within experimental error. 



CONCENTRATION AND COMPOSITION OF SOIL SOLUTION 221 

Discussion of the displacement method 

The results obtained seem to prove that the displacement method gives 
the true soil solution. It can be used on all soil classes and at a wide range 
of moisture contents. By using a long soil column small amounts of the soil 
solution have been obtained from Carrington silt loam at a moisture content 
of only 6 per cent. The moisture content at which heavy soils can be most 
conveniently worked is slightly below the optimum for plant growth. 

The method has several distinct advantages over other methods which are 
being used. One of its greatest advantages over the oil pressure method (18) 
is its simplicity and the fact that it does not require special apparatus. Ordi- 
nary glass percolators were entirely satisfactory for most of the work. If it 
is desirable to reduce the amount of alcohol required the displacement may be 
started with 200 or 300 cc. of alcohol and after this has penetrated the soil, 
water may be added to complete the displacement. 

The greatest advantage it has over water extracts is that it gives a more 
correct measure of the material in solution. In addition, the solution obtained 
is about twenty times as concentrated as the water extract. This greatly 
reduces the time required for evaporation in all determinations. Five cubic 
centimeters was generally sufficient for a colorimetric nitrate determination 
and 25 cc. for a total salt determination. 

The two main disadvantages of the method are the time required for dis- 
placement and the necessity of using a larger soil sample than is required by 
the water-extraction method. The time factor is best controlled by experi- 
ence and care in packing the soil. About five times as much soil must be 
used as is required for water extraction. 

The method seems to deserve much greater attention than it has received 
in the past. By its use considerable information may be obtained regarding 
the concentration, composition, and reaction of the true soil solution. It 
may also afford information that may be of value in studying results which 
have been obtained by water extraction and other methods. 

Results obtained with the displacement method indicate that at ordinary 
moisture contents the concentration of the soil solution is inversely propor- 
tional to the moisture content of the soil. This does not agree with the con- 
clusions which Bouyoucos and McCool made from results obtained with the 
freezing-point method. A study of the freezing-point method was therefore 
made to determine the cause of this disagreement. 

THE FREEZING-POINT METHOD 

The freezing-point method as a means of determining the concentration 
of the soil solution directly in the soil was first used by Bouyoucos and McCool 
(5, 6). It has since been used by Hoagland (13) in studying changes in the 
salt content of soils due to seasons and cropping. He compared results 
obtained by this method with those of Stewart (24) who used the water- 



222 F. W. PARKER 

extraction method. The two methods gave the same general indications 
regarding the changes which took place in the salt content of the soils, but 
the water-extraction method gave from 1.5 to 5 times as much total salts as 
was indicated by the freezing-point method to be actually in the soil solution. 

The freezing-point method as a means of measuring the concentration of 
the soil solution in the soil is based upon the principle that material in solu- 
tion causes a depression of the freezing point of the solvent. The assumption 
was made that the finely divided material of the soil does not affect the freez- 
ing-point of the soil solution. 

In determinations of the freezing-point depressions of soils at varying mois- 
ture contents, Bouyoucos and McCool (6) obtained results which, contrary to 
what would be expected, indicate that the concentration of the soil solution 
is not inversely proportional to the moisture content of the soil. The lower- 
ing of the freezing point of soils was found to increase approximately in geo- 
metric progression as the moisture content decreased in arithmetric progres- 
sion. This was explained by the following hypothesis: 

The hypothesis assumes that a portion of the water found in the soils is inactive and does 
not take part in dissolving the salts in the soil, and is removed from the field of action as 
far as the lowering of the freezing point is concerned. Under this assumption the increase 
of the freezing-point depression is a geometric progression as the percentage of water increases 
in an arithmetic progression is explained as follows: If a clay soil, for instance, causes 15 
per cent of water to become inactive, and this clay at 39 per cent of moisture produces a 
lowering of the freezing point of 0.075°C. and at 22 per cent 0.987°C, then at the former 
moisture content there is 24 per cent of water free or available to dissolve the salts in the soil, 
while at the latter water content there is only 7 per cent available for the same]; purpose. It 
would be natural, therefore, that the depression of the freezing point would be many times 
greater at the low moisture content than at the high, than would be expected from the dif- 
ference in the total moisture content, just as the experimental data really indicate. 

This hypothesis also assumes (and the assumption seems to have been proved) that the 
percentage of inactive water is greater at the low than at the high moisture content and 
tends to decrease from the former to the latter. 

Results obtained with the displacement method indicate that all of the 
water in the soil acts as a solvent and that there must be another explanation 
of the results obtained with the freezing-point method. 

The concentration of the soil solution at varying moisture contents as determined 
by the freezing-point and displacement methods 

It has already been shown in tables 4, 5, and 6 that, as determined by the 
displacement method, the concentration of the soil solution is inversely pro- 
portional to the moisture content of the soil. Freezing-point determinations 
were made at the same time on these soils. Having determined the freezing- 
point depression of the'soil and of the displaced solution, the value for K can 
be calculated for both, using the equation M.D = K. In each case M is the 
moisture content of the soil and D is the freezing-point depression of the 



CONCENTRATION AND COMPOSITION OF SOIL SOLUTION 



223 



soil or the displaced soil solution. If the concentration of the soil solution is 
inversely proportional to the moisture content K should be a constant. ■ If K 
is not a constant it indicates that the concentration of the soil solution is not 
inversely proportional to the moisture content or that there is another factor 
influencing the freezing-point depression. The value of K for the displaced 
solution and the soil should be the same if the freezing-point depression in 
both cases is caused entirely by the salts in the soil solution. If the values 
for K are not the same it indicates that there are other factors affecting the 
freezing-point depression of the soil. The results obtained with Miami silt 
loam are given in table 11. Results similar to those given were obtained with 
Plainfield sand and Carrington silt loam. 

The data show that the two methods give an entirely different indication 
of the concentration of the soil solution, particularly at the lower moisture con- 
tents, if it is assumed that the depression is due entirely to material in solution. 
At a moisture content of 10.30 per cent the freezing-point depression of the soil 

TABLE 11 
The freezing-point depression of Miami silt loam and the displaced soil solution at different 



moisture contents 



MOISTURE CONTENT 


FREEZING-POINT 
DEPRESSION 


FREEZING-POINT 
DEPRESSION 


K FOR SOIL 


K FOR SOLUTION 




of son. 


OF SOLUTION 






per cent 


"C. 


°C. 






10.30 


0.460 


0.039 


4.738 


0.401 


13.55 


0.257 


0.030 


3.482 


0.406 


17.25 


0.100 


0.022 


1.725 


0.379 


20.62 


0.057 


0.018 


1.175 


0.371 


29.41 


0.028 


0.013 


0.676 


0.382 


34.05 


0.016 


0.012 


0.544 


0.408 



indicates a concentration almost twelve times as great as is indicated by the 
freezing-point depression of the displaced soil solution. At the highest moisture 
content the two methods give nearly the same result. There are two possible 
explanations for the results obtained, viz., (a) the inactive or unfree water, 2 
which is not supposed to act as a solvent, may be displaced and dilute the 
other portion of the soil solution; (b) the soil may not cause water to become 
inactive as a solvent but the finely divided solid material of the soil may 
cause a depression of the freezing point in addition to that caused by materials 

in solution. 

The first explanation is plausible in that it is possible to displace small 
amounts of the soil solution at such low moisture contents that there would 
probably be no free water present. However, with this explanation it would 
be necessary to assume that unfree water is free to move capillarity. In fact, 
this assumption is necessary if the displacement method gives a true aliquot 

» In this paper the terms free and unfree or inactive water are used with the meanings 
attached to them by Bouvoucos and McCool (6), and by Bouyoucos (3). ( 



224 F. W. PARKER 

of the soil solution. It does not seem probable that a portion of the water 
would be unable to act as a solvent and at the same time be capable of capil- 
lary movement. Therefore, the second explanation may be more nearly 
correct than the first, as is further indicated in the following. 

It is well known that colloidal solutions have the same freezing point as 
pure water. However, such determinations are not comparable to determina- 
tions of the freezing-point depressions of soils in which the amount of liquid 
present is reduced until it is all in the capillary or film condition. In a review 
of the literature, the writer did not find any investigations in which a deliber- 
ate study was made of the effect of finely divided material on the freezing 
point when the amount of liquid was so reduced. Foote and Saxton (11, 12) 
however, in studying the forms of water in certain hydrogels by the dilatom- 
eter method, recognized that the hydrogels caused a depression of the 
freezing point of the capillary water. (They defined capillary water as that 
water which would not freeze at 0°C, but could be frozen at lower tempera- 
tures.) Van Bemmelen and other investigators (27) have shown that water 
in hydrogels has a low vapor pressure. Zsigmondy, Bachmann, and Steven- 
son (26) have shown that the same is true for alcohol and benzene in alcogels 
and benzolgels. If the vapor pressure of a liquid is lowered, its freezing point 
also is lowered. It therefore seemed probable that the solid material of the 
soil may cause a depression of the freezing point of the soil solution. The 
results shown in table 11 indicate that this is the case. In order to obtain 
more conclusive data on the question, a study was made of the effect of finely 
divided materials on the freezing point of water, benzene and nitrobenzene. 
A portion of the results are presented here, but for a more detailed discussion 
of the procedure and results the reader is referred to another article (20). 

In order to study the effect of finely divided materials upon the freezing 
point of liquids it is desirable to have the solid material as free as possible of 
substances soluble in the liquids. The materials used fulfilled this require- 
ment very well, as is indicated by the freezing-point depressions at the high- 
est moisture contents. 

The Fe(OH) 3 was prepared by precipitation with NH 4 OH from a cold 
dilute solution of the chloride. It was washed free of chlorides, air-dried and 
ground to pass a 200-mesh screen. The percentage of water in the Fe(OH) 3 
is expressed on the air-dry basis. In all other cases the percentage of liquid 
is expressed on the oven-dry basis. 

Baker's C. P. Al 2 Og was used. It contained some material soluble in water 
but nothing soluble in benzene or nitrobenzene. 

The freezing-paint depression of water in finely divided material 

The freezing-point depression of water in Fe(OH) 3 and Carrington silt loam 
was determined at varying moisture contents. The results are shown in 
table 12. 



CONCENTRATION AND COMPOSITION OF SOIL SOLUTION 



225 



The results indicate a considerable depression due to the solid material. 
The effect due to soluble material was probably small, especially in the case 
of the Fe(OH) 3 , since this material gave a depression of only 0.004°C. at a 
moisture content of 100 per cent. In order to explain the results obtained 
with Fe(OH) 3 by the hypothesis that it rendered part of the water unfree, 
it would be necessary to assume that at a moisture content of 15 per cent 
14.85 per cent of water was unfree and only 0.15 per cent of water was acting 
as a solvent as is indicated by the following calculations. Solving for K in 
the equation M.D - K when M is 100 and D is 0.004°C, the value of K is 
0.400. Taking this value for K and solving for M when the freezing-point 
depression is 2.668°C. one obtains 0.15 as the value of M. In this case M is 
the percentage of water which would be acting as a solvent at the moisture 
content at which a depression of 2.668°C. is secured. The inactive water 
would be obtained by difference and found to be 14.85 per cent. A similar 

TABLE 12 
The freezing-point depression of water in Fe(OH) 3 and in Carrington silt loam at varying 



moisture contents 




calculation for the soil shows that at a moisture content of 9.0 per cent it 
would be necessary to assume that only 0.60 per cent water was free and that 
8.40 per cent was unfree. 

The freezing-point depression of benzene and nitro-benzene in AWz and Carring- 
ton silt loam 

The use of organic liquids in which most inorganic salts are insoluble makes 
it possible to eliminate entirely the depression due to soluble materials. Ben- 
zene and nitrobenzene were chosen because they are readily obtained and 
freeze at a convenient working temperature. The results obtained with these 
liquids in Carrington silt loam and aluminium oxide are given in tables 13 

and 14. . ' r , 

The results are of the same order as was obtained with the same solid 

material and water. Since there is no material in solution it seems that the 



226 



F. W. PARKER 



only possible explanation of the results is that the solid material causes a 
depression of the freezing point of the liquids when they are in the film or 
capillary condition, but does not affect their freezing point at contents above 
saturation. If this is the correct explanation for the results obtained with 
these liquids it is undoubtedly the explanation for the results obtained with 
soils. It may therefore be concluded that at ordinary moisture contents the 
freezing-point depression of the soil solution in the soil is caused by two fac- 
tors, the material in solution, and the finely divided solid material of the soil. 

TABLE 13 

The freezing-point depression of benzene in Carrington silt loam and aluminium oxide 



CARRINGTON SILT LOAM 


ALUMINIUM OXIDE 


Benzene 


Freezing-point depression 


Benzene 


Freezing-point depression 


per cent 


"C. 


per cent 


°C. 


5.0 


0.660 


30.0 


1.337 


7.5 


0.355 


35.0 


0.682 


10.0 


0.150 


40.0 


0.492 


12.5 


0.060 


45.0 


0.326 


15.0 


0.033 


50.0 


0.212 


20.0 


0.025 


55.0 


0.115 


25.0 


0.010 


65.0 


0.052 


37.5 


0.000 


75.0 


0.030 






100.0 


0.000 



TABLE 14 
The freezing-point depression of nitrobenzene in Carrington silt loam and aluminium oxide 



CARRINGTON SILT LOAM 


ALUMINIUM OXIDE 


Nitrobenzene 


Freezing-point depression 


Nitrobenzene 


Freezing-point depression 


per cent 


°C. 


pet cent 


°C. 


12.5 


1.630 


50.0 


1.720 


15.0 


1.200 


60.0 


1.175 


17.5 


0.780 


70.0 


0.810 


20.0 


0.510 


80.0 


0.580 


25.0 


0.230 


90.0 


0.340 


30.0 


0.130 


100.0 


0.200 


37.5 


0.075 


150.0 


0.020 


50.0 


0.000 


200.0 


0.000 



The relation between the freezing-point depression due to solid material and that 
due to material in solution 

In order to determine whether or not the depression due to solid material 
and that due to material in solution are additive in their effect on the freezing 
point, samples of aluminium oxide were moistened with water and other 
samples were moistened with a sugar solution which had a freezing-point 



CONCENTRATION AND COMPOSITION OF SOIL SOLUTION 



227 



depression of 0.126°C. A sugar solution was used because there is no possi- 
bility of a chemical reaction between the sugar and aluminium oxide. B the 
two factors are additive the difference between the freezing-point depressions 
at any moisture content should be 0.126°C, the depression due to sugar. 
Adsorption may influence the results to some extent. The differences obtained 
are given in the last column of table 15. 

These results and others obtained when sugar solutions and a Ca(NUs)t 
solution were used in soils, kaolin, silica and ferric hydroxide, prove that the 
two factors are very nearly additive in their effect on the freezing point The 
differences found at the three lower moisture contents are easily within the 
limit of experimental error, which is quite large at low moisture contents. 
The presence of sugar did not affect the general order of results 

The results afford further evidence that the great increase in the freezing- 
point depression at the lower moisture contents is not due to part of the water 
being withdrawn from the role of a solvent by the solid material. If the 

TABLE 15 
The freezing-point depression of water and a sugar solution in aluminium oxide at different 

moisture contents 



MOISTURE CONTENT 



per cent 
25.0 
30.0 
35.0 
40.0 
50.0 
75.0 
100.0 



FREEZING-POINT 
DEPRESSION WITH WATER 


FREEZING-POINT 

DEPRESSION WITH 

SOLUTION 


°C. 


°C. 


2.118 


2.290 


1.227 


1.312 


0.650 


0.740 


0.370 


0.500 



0.220 
0.075 
0.053 



0.344 
0.195 
0.173 



FREEZING-POINT 

DEPRESSION DUE TO 

THE SUGAR 

°C. 

0.172 
0.075 
0.090 
0.130 
0.124 
0.120 
0.120 



aluminium oxide had rendered any of the water unfree the solution would 
have been greatly concentrated at the lower moisture contents and the depres- 
sion due to the sugar would have been many times that shown in the table. 
The depression of the freezing point of water at 25 per cent was forty times 
as great as at 100 per cent. If this had been caused by part of the water 
being withdrawn from the r6le of a solvent, and the same amount had been 
withdrawn when the sugar solution was added the depression of the sugar 
solution at 25 per cent would have been 6.920°C. instead of 2.290 C. The 
depression due to the sugar alone at this moisture content would have been 
4.802°C. instead of only 0.172°C, the experimental value. 

The freezing-point depression of soils at their moisture equivalent 

The freezing-point depression of soils at medium to low ^ moisture ^contents 
is caused in large part by the solid material. The force which holds the water 
on the soil particles probably causes the freezing-point depression. If a num- 



228 



F. W. PARKER 



ber of soils are subjected to the same centrifugal force, and come to an equilib- 
rium with this force, they will retain different percentages of water. These 
different percentages of water which are retained will be held with equal 
forces in the different soils. Since this same force probably causes the freez- 
ing-point depression, it should be possible to reduce all soils to the same 
freezing-point depression, after the removal of soluble salts, by subjecting 
them to the same centrifugal force. 

In a determination of the moisture equivalent of soils the soil is subjected 
to a centrifugal force of 1000 times gravity. The moisture content after cen- 
trifuging is that at which the force of attraction between the soil and water is 
equal to this centrifugal force. In this manner the force holding water in 
different soils may be brought to a uniform value. Therefore the freezing- 
point depression of the soils, due to solid material, should be equal at the 
moisture contents represented by their moisture equivalents. 

TABLE 16 
The freezing-point depression of washed soils at their moisture equivalent 



Carrington silt loam 

Knox silt loam 

Mellen loam 

Superior clay 

Plainfield sand 

Miami silt loam. . . . 

Silty clay loam 

Fine sandy loam 

Peat 

Kaolin 

Silica 

Aluminium oxide . . . 



MOISTURE 


FREEZING-POINT 


EQUIVALENT 


DEPRESSION 




•c. 


21.57 


0.055 


25.40 


0.057 


16.39 


0.053 


21.84 


0.061 


4.73 


0.076 


26.47 


0.052 


33.29 


0.061 


12.49 


0.057 


111.60 


0.061 


38.12 


0.046 


19.14 


0.057 


21.56 


0.043 



In order to determine the freezing-point depression due to solid material it 
is necessary to remove the soluble material as far as possible. One-hundred- 
gram samples of different soils, silica, kaolin and aluminium oxide were washed 
with 1200 to 1500 cc. of distilled water to remove soluble salts. The samples 
were then dried in an electric oven at 105°C. The moisture equivalent was 
determined in the usual manner. After centrif uging the freezing-point deter- 
minations were made on the soils. The speed of the centrifuge was slightly 
less than that which gives a force of 1000 times gravity. This caused slightly 
high results for the moisture equivalent and hence low results for the freezing- 
point depression, due to solid material, at the true moisture equivalent. There 
were undoubtedly several sources of error, such as the incomplete removal of 
the soluble material, puddling in making the determination of the moisture 
equivalent, and evaporation in transferring the soil from the moisture cups 
to the freezing-point tubes. The results are shown in table 16. 



CONCENTRATION AND COMPOSITION OF SOIL SOLUTION 

The results indicate that at the moisture equivalent the depression of the 
freezing point due to solid material is very nearly the same in different soils 
and certain artificial materials. This can be explained only by the assump- 
tion that the same force which retains the moisture causes the freezing-point 
depression. The values are not exactly the same but are within experimental 
error. The low values for kaolin and aluminium oxide are probably due to 
the fact that these materials pack very tightly in the centrifuge preventing 
the water from being readily thrown out. The high result for the Plainfield 
sand may be due to the extreme readiness with which the water is removed 
from such a coarse soil. 

The results indicate that the freezing-point method could be used to deter- 
mine the salt content of soils at their moisture equivalent. At the moisture 
equivalent the depression due to solid material is probably a constant, about 
0.050°C. By determining the freezing-point depression of a soil at its mois- 
ture equivalent and subtracting this constant, the freezing-point depression 
due to soluble material would be obtained. In using such a procedure great 
care should be taken that the true moisture equivalent is used in all cases, for 
a slight error in the moisture content would decidedly affect the freezing- 
point depression due to solid material. This procedure is rather long, so it is 
doubtful if it would be of much value. If the freezing-point method is used 
it would be more convenient and probably more accurate to make the deter- 
minations at moisture contents above saturation, entirely eliminating the 
depression caused by the solid material. 

Discussion of the freezing-point method 

The freezing-point method does not give a measure of the concentration of 
the soil solution in the soil at ordinary moisture contents, for it has been 
shown that finely divided material causes a depression of the freezing point 
of a liquid in the film or capillary condition. The force holding the liquid on 
the solid material and causing the freezing-point depression is adhesion. 
When the amount of water in the soil is increased a point is reached at which 
some of the soil solution is so distant that this force no longer affects its freez- 
ing point. This point is probably the point of saturation. Probably at any 
moisture content below saturation the solid material causes a depression of 
the freezing point of the soil solution. At moisture contents above saturation 
the depression becomes due entirely to material in solution. 

The freezing-point method has been used by Bouyoucos and his associates 
to determine the lime requirement of soils (1), the velocity of reactions between 
soils and chemical reagents (4), the solubility of soils (2), and the absolute 
salt content of soils (7). In these investigations the moisture content was 
always very high, varying from 66 to several hundred per cent. At those 
moisture contents the depression is due entirely to materials in solution and 
the method gives a satisfactory measure of the soluble material present. It 
is well adapted to such studies and used under these conditions has given 
valuable results. 

BOIL SCIENCE, VOL. XII ,NO. 3 



230 F. W. PARKER 



SUMMARY 



It is desirable in studying problems of soil fertility, plant nutrition and 
related subjects to have a method with which the true soil solution may be 
obtained from a soil at ordinary moisture contents in sufficient quantities for 
analytical work. In a review of the literature it was found that Ischerekov 
(15), using the displacement method, obtained results which indicate that the 
method gives the true soil solution in quantities sufficient for most purposes. 
Hence it seemed desirable to make a study of the method and compare it 
with other methods which are now being used in studying the concentration 
and composition of the soil solution. 

The method consists of packing the moist soil in a cylinder provided with 
an outlet at the bottom. Ethyl alcohol is then poured on top of the soil 
column and as it penetrates the soil it displaces some of the soil solution 
which forms a zone of saturation below the alcohol. This zone increases in 
depth as it is continually forced downward by the alcohol. When the satu- 
rated zone reaches the bottom of the soil column the clear soil solution, free 
of alcohol, drops from the soil as gravitational water. 

A study was made of the effect of different displacing liquids on the time 
required for displacement, the percentage of the soil solution displaced and 
the composition of the displaced solution. The concentration of successive 
portions of the displaced soil solution was determined and also the concen- 
tration of the soil solution obtained from the soils at different moisture con- 
tents. The amount of total salts, nitrates, and calcium obtained from the 
soil by displacement was compared with the amount secured from the soil by 
water extraction. 

Results obtained with the displacement method did not agree with the 
conclusions of Bouyoucos and McCool (6), drawn from a study of the freez- 
ing-point depressions of soils, with regard to the concentration of the soil 
solution at different moisture contents and the forms of water in the soil. 
Therefore a study was made of the freezing-point method and factors affect- 
ing the freezing-point depression of the soil solution in the soil. The effect of 
finely divided material on the freezing point of water, benzene and nitroben- 
zene was studied. A summary of the results and conclusions is given below. 

(a) Ethyl alcohol was found to be more satisfactory as a displacing liquid 
than water, methyl alcohol, acetone, or liquids non-miscible with water. 

(b) The composition of the soil solution obtained by displacement was not 
influenced by the displacing liquid used. 

(c) Successive portions of the displaced solution gave the same freezing- 
point depression and contained the same amount of total salts. 

(d) The concentration of the displaced solution was found to be inversely 
proportional to the moisture content of the soil. 

(e) The displacement method gave the same amount of nitrate nitrogen 
and approximately the same amount of total salts as a 1 : 5 water extraction 
of the soil. 



CONCENTRATION AND COMPOSITION OF SOIL SOLUTION 231 

(f ) The method seems to be well adapted to a study of the composition and 
reaction of the soil solution under any condition. 

(g) Finely divided material was found to cause a depression of the freezing 
point of water, benzene, and nitrobenzene when the amount of liquid was 
reduced until it was in the film or capillary condition. 

(h) The freezing-point method does not give a measure of the concentration 
of the soil solution directly in the soil at ordinary moisture contents of the 

soil. 

(i) At high moisture contents, probably only above saturation, the freez- 
ing-point method gives a measure of the concentration of the soil solution. 

(j) The freezing-point depression due to solid material at the moisture 
equivalent was found to be very nearly a constant for a number of soils. 

(k) A soil does not cause a considerable amount of water to be removed 
from the role of a solvent, as has sometimes been assumed. 

A subsequent article will be devoted to the classification of the soil moisture 

REFERENCES 

(1) Bouyoucos, G. J. 1916 The freezing point method as a new means of determining 

the nature of soil acidity and the lime requirement of soils. Mich. Agr. Exp. 
Sta. Tech. Bui. 27. 

(2) Bouyoucos, G. J. 1919 Rate and extent of solubility of soils under different treat- 

ments and conditions. Mich. Agr. Exp. Sta. Tech. Bui. 44. 

(3) Bouyoucos, G. J. 1921 A new classification of the soil moisture. In Soil Sci., v. 

11, no. 1, p. 33^9. . 

(4) Bouyoucos, G. J., and Laudeman, W. A. 1917 The freezing point method as a new 

means of studying the velocity of reaction between soils and chemical reagents 
and the behavior of equilibrium. Mich. Agr. Exp. Sta. Tech. Bui. 37. 

(5) Bouyoucos, G. J., and McCool, M. M. 1915 The freezing point method as a new 

means of measuring the concentration of the soil solution directly in the soil. 
Mich. Agr. Exp. Sta. Tech. Bui. 24. 

(6) Bouyoucos, G. J., and McCool, M. M. 1916 Further studies on the freezing-point 

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(7) Bouyoucos, G. J., and McCool, M. M. 1918 Determining the absolute salt con- 

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(8) Briggs, L. J., and McCall, A. G. 1904 An artificial root for inducing capillary 

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(9) Cavers F G 1914 Gola's theory of Edaphism. In Jour. Ecol., v. 2, p. 217. 

(10 Davis R. O. E., and Bryan, H. 1910 An electrical bridge for the determination 
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(11) Foote, H. W., and Saxton, B. 1916 The effect of freezing on certain inorganic 

nvdrogels I. In Jour. Amer. Chem. Soc, v. 38, no. 3, p. 588-609. 

(12) Foote, H. W., and Saxton, B. 1917 The effect of freezing on certain inorganic 

hydrogels: II. In Jour. Amer. Chem. Soc, v. 39, no. 6, p. 1103-1125. 

(13) Hoagland D. R. 1918 The freezing-point method as an index of variations in tne 

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(14) Hoagla^D.R., Martin, J. C, and Stewart, G. R. 1920 Elation of the soil solu- 

tion to the soil extract. In Jour. Agr. Res, v. 20, no. 5, p. 381-395. 



232 F. W. PARKER 

(15) Ischerekov, V. 1907 Obtaining the soil solution in an unaltered condition. In 

Zhur. Opuitn. Agron. (Russ. Jour. Exp. Landw.), v. 8, p. 147-166. 

(16) Ltpman, C. B. 1918 A new method of extracting the soil solution. Univ. Cal. Pub. 

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(17) Mitscherlich, E. A. 1907 Eine chemishe Bodenanalyse fur pflanzenphysiologische 

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(18) Morgan, J. F. 1916 The soil solution obtained by the oil pressure method. Mich. 

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(19) Northrup, Z. 1918 The true soil solution. In Science, v. 47, p. 638-639. 

(20) Parker, F. W. 1921 The effect of finely divided material on the freezing point of 

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(21) Ramann, E., Marz, S., and Bauer, H. 1916 The soil solution obtained by the 

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(22) Schxoesing, Th. 1866 Sur l'analse des principes solubles de la terre vegetale. In 

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(23) Schreiner, O., and Failyer, G. H. 1905 Colorimetric, turbidity, and titration 

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(24) Stewart, G. R. 1918 Effect of season and crop growth on modifying the soil extract. 

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(25) Van Suchtelen, F. H. H. 1912 Methode zur Gewinnung der naturlichen boden- 

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(26) Zsigmondy, R., Bachmann, W., and Stevenson, E. J. 1912 Ueber einen Apparat 

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New York. 



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